Oil based stone composites using anhydride containing compounds suffer from toxicity, discoloration, or hardness issues. For example, methylhexahydrophthalic anhydride is considered a health hazard even at low levels. Other anhydrides darken the final composite product and may cure non-uniformly due to their solid states.
Example stone composite fabrication processes involve low molecular weight polyester with unsaturated moieties mixed with styrene monomer as a reactive diluent, heated in the presence of suitable catalysts (e.g. a free radical initiator), where the excess unreacted styrene has to be removed from the system. As another example process, copolymers of methyl methacrylate oligomers are used as a binder in the presence of a reactive diluent like methyl methacrylate monomer, where the system is cured in the presence of free radicals generating peroxide initiators at high temperatures to make a hard composite product. In both of these examples and other process, the excess unreacted diluent has to be removed from the system. These reactive diluents are both highly toxic and flammable, and therefore create a hazardous work environment. As another example, enclosed and self-contained equipment to properly handle vapors from acrylic and styrene monomers is capital intensive in addition to its toxicity concerns for workers.
Various epoxidized materials are known (e.g. Bisphenol based epoxies), but these have limited environmental resistance and tend to chalk and yellow over time. What's more, the raw materials used to manufacture these chemicals are environmentally detrimental.